1. Field of the Invention
The present invention relates to a lens driving apparatus disposed for moving lens groups in an enlarger, a telescope and a microscope, etc., and more particularly, to a lens driving apparatus for moving a plurality of movable lens groups such as zoom lens, etc., in a predetermined relationship.
2. Related Background Art
A cylindrical cam has generally hitherto been employed for driving and positioning the movable lens groups in predetermined positions in the enlarger, the telescope and the microscope, etc.. A lens position is controlled by regulating a rotary angle of the cylindrical cam.
If the movable lens groups are required to move at a high speed, a feed screw is also employed in place of the cylindrical cam.
When driving the movable lens group by use of the cylindrical cam, however, it is required that the cylindrical cam be rotated. Hence, a loss in driving force is large, and a loss due to frictions is also large. A problem is therefore a difficulty of correspondance to a high durability and a high-speed drive of the movable lens group.
Further, working the cylindrical cam is difficult and requires high costs. Besides, there arises a problem, wherein if the cylindrical cam is once worked, modification and compensation after assembly are arduous.
On the other hand, when driving the movable lens group by use of the feed screw, driving sources are needed for the plurality of movable lens groups, respectively. Moreover, the respective movable lens groups are moved precisely and correlatively. This requires control for correlating the movable lens groups, resulting in a problem such that the structure increases in costs and becomes complicated.
Additionally, in the case of the feed screw, the movable lens group can be driven at a high velocity. The feed screw itself is, however, expensive. Besides, the feed screw presents a problem in which moving members impinge on each other, or the moving member collides with a fixing member at both ends of a movable range of the lens groups due to inconvenience or the like in terms of driving control.
Then, a stop position accuracy can not be, as a matter of course, be ensured in such a case. There arises, however, a problem wherein an element for absorbing the impact and stopping them is needed to prevent a mechanism from being broken.
Now, it is considered that the lens groups are drive by employing a link mechanism. In this case, however, there exists a problem in which a moving quantity of the movable lens group is hard to adjust.